1. Field of the Invention
The present invention relates to backplanes for electronic systems, and, more particularly, to an apparatus and method for grounding the backplane to the chassis of the electronic system when the backplane is inserted into the chassis.
2. Description of the Related Art
Modern computers often include multiple hard-disk drives, flexible-disk drives, CD-ROM drives, and the like. These drives include motors and mechanisms for spinning the storage media and for moving read heads or read/write heads, and also include circuitry for controlling mechanical movement as well as the transfer of data. For example, a computer system may include a RAID (Redundant Array of Inexpensive Disks) subsystem which includes three or more hard-disk drives.
In computer systems having RAID subsystems, the disk drives are mounted on separate frames or trays and inserted side-by-side into a cavity within the computer. The internal sheet metal chassis of the computer defines guides for aligning connectors on the drives with mating connectors on a rigid backplane. The backplane defines an inner wall of the cavity and provides electrical interconnections to and from the mating connectors. The backplane may be a passive backplane, or it may include electronic components which transfer data to and from the disk drives and which control the disk drives.
Typically, the backplane is constructed of an insulating rigid substrate having the electrical connections formed on one or more layers. The backplane is firmly attached to the internal chassis of the computer, typically with threaded fasteners. The cavity defined on the sides by sheet metal panels of the internal chassis and on the inner wall by the backplane, is termed the "drive cage."
Typically, a computer system having a RAID subsystem has a so-called "tower" configuration wherein the computer system is taller than it is wide, as opposed to a desktop system which is generally wider than it is tall. One aspect of a RAID subsystem is that a disk drive can be readily replaced if it fails during operation. Thus, a RAID subsystem is typically mounted in the computer system so that the disk drives can be extracted and inserted through the front of the computer system cabinet. In order to accommodate this feature, the backplane for the RAID subsystem is mounted with the backplane perpendicular to the side walls of the computer system.
In operation, the disk drives generate substantial electromagnetic interference (EMI) and radio frequency interference (RFI), and are susceptible to electrostatic discharge (ESD). It is important to provide an adequate grounding system to suppress EMI and RFI and to prevent damage from ESD. In particular, the backplane in a computer system must be securely grounded to the internal chassis. This is typically accomplished with the use of fasteners extending through apertures in the backplane and secured within threaded holes in conductive components of the chassis. The fasteners extend through apertures surrounded by conductive ground pads in the backplane. The fasteners also ensure that the backplane is rigidly attached at the inner end of the drive cage so that the various drives can be inserted and pushed against the backplane to couple the mating connectors.
The use of fasteners to attach the backplane to the computer chassis has several drawbacks. For example, positioning and engaging fasteners add complexity to the assembly process. Most of the inner components of the computer are installed through one of the large side panels. The components are designed to be installed straight in through the panel, with the locations being readily accessible. On the other hand, as discussed above, the backplane is mounted perpendicular to the plane of the side panel, and thus the fasteners extend in parallel with the side panel. This requires an assembly procedure wherein the worker has difficulty in accessing and driving the fasteners into place. Moreover, after other components are installed in the computer system, the backplane fasteners may become inaccessible without removing other components of the computer system. The inaccessibility of the fasteners increases the difficulty of maintenance. Another drawback with fastening the backplane to the drive cage is the potential for misalignment between the mating electrical connectors of the backplane and the disk drives. This comes about if the holes for the fasteners in either the backplane or the computer chassis are slightly out of alignment. In other words, to ensure that the mating connectors of the backplane and disk drives accurately align, the mounting holes in the backplane must be precisely located with respect to the backplane connectors, and the mounting holes in the chassis must be precisely located with respect to the disk drive guides. Close tolerances for these mounting holes thus ensure the accurate alignment of the connectors, which adds expense in the manufacturing process.
In view of the foregoing drawbacks, there is a need for an alternative to securing the backplane to the drive cage using fasteners.